...which is why, as an idiom, it's wise to disconnect the success flag from the return value of the thing_that_may_fail(). I'm glad I'm not alone in seeing merit in the clarity that comes from decoupling the thing that may fail from the idiom that tests it.
The point to "eval "possible_failure(); 1"" is that we're not concerned with possible_failure()'s return value, we're concerned whether or not it threw an exception. We shouldn't have to look up and infer what its return value will be, we should simply test whether it threw an exception or not. That's where 1;" or warn "Woops!"; comes in.